1. Field of the Invention
The present invention relates to a mounting structure for an air separator that supplies air for cooling a rotor blade in a gas turbine.
2. Description of the Related Art
A mounting structure for an air separator includes an air separator and a rotor blade rotary disk. The mounting structure takes a portion of compressed air that is compressed by a compressor, and supplies the compressed air as cooling air to the rotor blade.
FIG. 8 is a cross section of a gas turbine around a conventional air separator disclosed in, for example, Japanese Patent Application Laid-open No. H11-013408. The gas turbine includes a first stage stator blade 4 and a first stage rotor blade 5, an air separator 3-2, a rotor 1, a compressor (not shown), and a cooler (not shown). A portion of air compressed by the compressor and cooled by the cooler is taken in from a rotor side opening 8 via a clearance 9 between the air separator 3-2 and the rotor 1, and further introduced into inside of the first stage rotor blade 5 via radial holes 10 and cooling air holes 11 of a rotor blade rotary disk 2 to air-cooled the first stage rotor blade 5. The rotor blade rotary disk 2 having the first stage rotor blade 5 embedded at a peripheral end thereof is mounted on the rotor 1 so that the rotor blade rotary disk 2 is rotated together with the rotor 1. On the other hand, the air separators 3-1 and 3-2 are constituted of a pair of cylindrical members separated from each other, one ends thereof being provided with flanges 20-1 and 20-2 for fixing the air separators 3-1 and 3-2 and the other ends thereof being positioned adjacent to the opening 8 for introduction of cooling air. One air separator 3-1 is fixed to the rotor 1 via the flange 20-1 by a bolt and nut set 6-1, while the other air separator 3-2 is fixed to the rotor blade rotary disk 2 via the flange 20-2 by a bolt and nut set 6-2, so that these separators are rotated integrally with the rotor 1 and the rotor blade rotary disk 2. A portion of cooling air fed from a compressor (not shown) via an air duct 43 is taken in from the opening 8 formed between sealing portions 41 and 42 into the air separator 3-2. Furthermore, the cooling air is supplied to a cooling air hole 11 provided in the rotor blade rotary disk 2 through the clearance 9 provided between the rotor 1 and the air separator 3-2, and is also supplied to the radial hole 10 through an air hole (not shown) provided in the flange 20-2 of the air separator 3-2, so that the air is finally supplied to respective rotor blades.
FIG. 9 is a perspective of the separator 3-2. In the flange 20-2 of the air separator 3-2 fixed to the rotor blade rotary disk 2 by the set of a bolt and a nut 6-2, when leakage of cooling air taken in via the clearance 9 between the rotor 1 and the air separator 3-2 occurs, the cooling air cannot be supplied up to a distal end of the rotor blade sufficiently, which can damage the rotor blade due to cooling deficiency. Therefore, an outer face of the rotor blade rotary disk 2 and a contact face of the flange 20-2 are brought in close contact with each other by fastening the flange 20-2 to the rotor blade rotary disk 2 using the bolt and nut set 6-2, and sealing is performed by a fastening force of the bolt and nut set 6-2, so that occurrences of air leakage are prevented at the flange.
On the other hand, when the gas turbine runs again after stopping, a hot start operation is often performed. The term “hot start operation” means an operation for causing a gas turbine (apparatus) to run again while respective portions in the gas turbine are still relative hot (for example, about 200° C.) after the apparatus is stopped.
Operation statuses during the hot start operation will be explained with reference to FIGS. 10 and 11. FIG. 10 is a graph of change of a turbine revolution speed during the hot start operation from an operation start time along with time elapse. In FIG. 10, vertical axis represents the turbine revolution speed, while horizontal axis represents time elapsed from the operation start time. Main items of the operation statuses from the operation start up to a steady operation are represented on the horizontal axis. Purge operation with a constant turbine revolution speed (for example, 500 to 600 revolutions per minute (rpm)) within the apparatus is conducted for a predetermined time from the gas turbine operation start. Thereafter, a combustor is ignited and the turbine revolution speed is further increased up to a rated speed (for example 3600 rpm), while increasing the amount of fuel. After the turbine revolution speed reaches the rated speed, output is further increased by increasing fuel so that it is shifted to the steady operation (maximum load operation). The hot start operation of the gas turbine is performed in this manner.
Change of a temperature of cooling air along with time elapse corresponding to the hot start operation of the gas turbine will be explained with reference to FIG. 11. In FIG. 11, vertical axis represents a temperature of cooling air leaving the cooler (not shown) from the compressor (not shown) to flow in the air separator, while horizontal axis represents time elapsing from an operation start. After the gas turbine is activated, during the purge operation, the temperature is kept about 50 to 60° C. After the combustor is ignited, an air temperature also rises along with increase in turbine revolution speed, and the air temperature reaches about 150 to 160° C., when the revolution speed reaches the rated speed. Thereafter, although the air temperature further rises along with increase in the amount of fuel for increasing output in the combustor, the temperature is kept at a predetermined temperature of about 200° C., when the operation reaches a maximum load operation. The temperature of cooling air flowing in the air separator changes rapidly from the operation start in this manner, while the cooling air flows from the opening 8 into the air separator 3-2 to be supplied to the radial hole 10 and the cooling air hole 11 via the clearance 9 and fed to respective rotor blades, as shown in FIG. 8.
However, because temperature change of cooling air flowing in the air separator is large during the hot start operation of the gas turbine, the following problems can occur. That is, because the air separator is constituted of a cylindrical member thinner than the rotor blade rotary disk that is a large-sized member, a heat capacity of the former is smaller than of the latter. As shown in FIG. 12, therefore, a temperature of the air separator drops along with time elapse in an initial stage of the hot start operation and it becomes the lowest temperature just after ignition; however, temperature drop of the rotor blade rotary disk is relatively small. That is, the flange of the air separator causes thermal contraction toward a radially central direction along with the temperature drop. On the other hand, because temperature drop of the rotor blade rotary disk is small, its thermal contraction in the radial direction hardly occurs. This results in relative displacement on a contact face between the flange and the rotor blade rotary disk in the radial direction due to a difference in degree of thermal contraction between the both. Furthermore, because the fastened bolt is maintained at the same high temperature as that of the rotor blade rotary disk, it is kept in an expanded state, however, the temperature of the flange decreases due to the cooling air and it shrinks in a thickness direction thereof. Therefore, the bolt itself is put in a relatively expanded state so that its fastening force is reduced. That is, the relative displacement in a radially central direction and the reduction in a bolt fastening force due to the difference in thermal contraction are simultaneously generated on a contact face of the flange and the rotor blade rotary disk along with the temperature lowing of the flange, so that air leakage easily occur on the contact face of the flange. That is, when a rapid temperature change is caused, as in such a hot start operation, the method for performing sealing using the bolt fastening force has such a problem that air leakage easily occurs and vibrations of the air separator are easily generated.